The present invention relates to ultrasonic imaging techniques for obtaining information about tissue elasticity and in particular to a method of rapidly acquiring three-dimensional elasticity reconstructions useful, for example, during RF ablation.
Elastography is an imaging modality that reveals the stiffness properties of tissues, for example, axial strain, lateral strain. Poisson's ratio, shear wave velocity, shear and Young's moduli, or other common stiffness measurements. The stiffness measurements may be output as quantitative values or mapped to a gray or color scale to form a picture over a plane or within a volume.
Generally, stiffness is deduced by monitoring tissue movement under an applied quasi-static or dynamic force or deformation. The monitoring may be done by any medical imaging modality including computed tomography (CT), magnetic resonance imaging (MRI), and ultrasonic imaging. Elastography of this type is analogous to a physicians palpation of tissue in which the physician determines stiffness by pressing the tissue and detecting the amount that the tissue yields under pressure.
In “dynamic” elastography, a low frequency vibration is induced in the tissue and the velocity of the resulting compression/shear waves are tracked and measured, for example, using ultrasonic Doppler detection. In “quasi-static” elastography, two images of the tissue are obtained at different states of compression, typically using the ultrasonic transducer as a compression paddle. Displacement of the tissue between the two images is used to deduce the stiffness of the tissue.
Ideally, elasticity data is acquired over a volume of interest in the tissue, U.S. patent application Ser. No. 13/780,880, filed Feb. 28, 2013, assigned to the same assignee as the present invention and hereby incorporated by reference, describes a system for volumetric ultrasound acquisition which obtains data in a series of radially extending planes positioned at different angles about a common axis.
With most acquisition patterns, spatial data must be interpolated to regular voxel points along a regular grid so that the data may be displayed through projections as pixels on a display monitor. In the acquisition pattern of radially extending planes described above, data on any of the planes may be first interpolated to regular grid locations within the plane and then interpolation may be conducted between the interpolated data of different planes.
The spatial data may be relatively noisy and accordingly, within each plane, the spatial data may first be fit to a model, for example, extracting trends from the data that reduce image artifiicts caused by noise.